Preparation of crystalline materials



March 5, I946. G. H. FOSTER ETAL 5 PREPARATION OF CRYSTALLINE MATERIALS Filed Oct. 30, 1941 Patented Mar. 5, 1946 umrso sr F l E PREPARATION OF CRYSTALLINE MATERIALS George H. Foster, Stamford, and Emil F. VVilliams, Old Greenwich, Conn, American Cyanamid Company,

assignors to New York,

.3 Claims.

This invention relates to a process for preparing crystalline and crystallizable substances in a very fine state of subdivision, and contemplates such improvements and refinements in the production of such substances as result in a product having certain highly desirable properties and characteristics. More particularly it embraces the production of nitroguanidine and similar substances in an extremely minute crystalline state.

Heretofcre it has been difficult and frequently impossible to prepare such crystalline substances as, for example, nitroguanidine in the form of discrete crystals of a size less than about 15 microns in width or less than about 300 or 400 microns in length. The usual methods of crystallization or recrystallization, even when supplemented by subsequent grinding or ball-milling in a porcelain mill ordinarily result in the production of much larger crystalline structures. Moreover, the grinding of such materials as are explosive in nature is a distinct hazard both to the workmen engaged therein and to the plants carrying out the process. In addition, however,

such grinding simultaneously effects but a slight decrease in particle size.

It is an object of this invention to provide a method for the production of nitroguanidine of extremely small size in an efficient and economical manner. troguanidine in the form of'small and uniformly very fine crystals. More specifically, it is an object of this invention to control the crystal habit, particularly the size, shape and form of crystals of nitroguanidine and to provide certain improved methods for the manufacture of nitroguanidine which facilitate the obtainment of a product having a novel and desirable crystal habit. It is also an object hereof to obtain, with the aid of a chemical modifier, crystals of nitro- A further object is to prepare ni-' guanidine which are smaller and finer than those ordinaril obtained in the course of a conventional physical crystallization. A further object is to provide a method wherein, by the addition of a wetting agent or dispersing agent before the final drying step, the ultimate individual crystals are obtained in such a state as to be free from branching and aggregation and remain as separate particles when stored for prolonged periods in the dry state. Still other and further objects will become apparent upon reading the following description wherein a number of specific embodiments of the invention are given.

This invention is based principall upon the discovery that a coating or shell is formed by an included amino or similar nitrogen containing compound, on and about the minute nucleus of a precipitated crystalline substance, such as nitroguanidine, immediately upon precipitation or formation from its solutions provided small amounts of such an amino or similar nitrogen containing compound are present in solution during the precipitation.

The best conditions for the physical crystallization of soluble materials such as nitroguanidine have heretofore been attained by preparing a saturated solution of the nitroguanidine in hot water and then suddenly cooling the solution as by spray cooling, chilling, or discharging it into an ice cold liquid or by utilizing equivalent means for cooling the nitroguanidine solution. This invention embodies the addition of a small amount of a foreign substance, such as an amino or similar nitrogen containing compound, to the hot aqueous solution of nitroguanidine before its crystallization, and precipitating the solute therefrom in the form of a pure nitroguanidine in such a fine degree of subdivision as has been impossible to obtain heretofore, b the conventional methods.

In its broadest aspects, the method herein disclosed contemplates the modification of crystal habit, particularly particle size, by the addition of any one of a number of diiierent foreign substances to a solution of nitroguanidine before recrystallization and allowing this additive to remain in solution during the recrystallization. Such a method can be carried out in accordance with the principles of this invention by rapidly cooling a saturated solution of nitroguanidine to which has been added a small amount of a modifying compound or addition agent, e. g. 1% of a material containing an amino or a similar nitrogen containing group such as ethylene diamine, diethylene triamine, triethylene tetramine, and tetraethylene pentamine; amino acids, including glue, casein and the like. In addition to the above substances a synthetically prepared Wetting agent also preferably containing an amino group, such as lauryl biguanide acetate; 1,3-diethylol, 5-butyl biguanide diacetate; monoethylol cyanamide condensed with ethylene diamine; acylated amides of polyethylene polyamines and the like, among others, may be used as the addition agent.

More particularly, it has been found that nitroguanidine crystals having a cross section of less than 5 microns and a length of less than microns can be prepared by the addition of ethylene diamine to a nitroguanidine solution in an amount of 0.3% based on the total solution. Similar effects can be obtained by the addition of about 0.6% of diethylene triamine, triethylene tetramine and tetraethylene pentamine, individually or as a mixture. In their order of effectiveness for the purposes of this invention these individual compounds may be tentativel arranged in the following sequence: diethylene triamine triethylene tetramine tetraethylene pentamlne. The addition of ethylol dodecyl bi guanide acetate up to about 1.0% is also effective. Optimum results are obtained when the pI-I of the solution is adjusted to about 8. Preferably,

acetic acid can be used to attain this pH after theaddition of the ethylene diamine.

In some instances the use of individual additives has been found to yield a crystalline product which may necessitate additional processing. Thus, for example, ethylene diamine may result in a product which dries to form hard lumps or aggregates which are not readily broken up by line precipitates, it is believed that the modifying compound shows preferential adsorption on certain crystallographic planes; covering portions or all of the external surface of each crystal nucleus as formed. This adsorbed material efiect'ively prevents further crystal growth as by accretion on the first formed crystal nucleus. Furthermore, there is a possibility that the solubility of the nitroguanidine at the crystallization temperature is decreased'by the addition agent; This increases the number of crystal nuclei formed and correspondingly decreases their size. result of the addition of the above modifying compounds to a hot aqueous solution of nitroguanidine of about 7.5% concentration and subjecting the solution to a subsequent very rapid cooling, as by spraying or otherwise cooling the same, crystals of nitroguanidine having a size of the order of 2.5 microns in width and 20 micronsin length are obtained. An additional advantage of the process of this invention is found in that the product thus prepared is far more stable than a similar product crystallized in the absence of such a modifying compound. This may be attributed to the addition of amines which effectively neutralize any acidity developed in the nitrogu anidine as a result of its decomposition during storage. This stability is due principally to the factthat the fine crystals ofnitroguanidine contain minute amounts of the addition agent. Depending on the addition agent used, the crystals can be rendered more or less readily dispersible in water or other media.

The improvements and advantages of the present invention are more readily appreciated when considered in conjunction with the appended drawing, in which:

Fig. 1 is a reproduction of a photomicrograph of nitroguanidine crystals prepared without a modifier and more particularly referred to in Example 3; and

Asa

Fig. 2 is a reproduction of a photomicrograph o'fnitroguanidine crystals prepared in accordance with the method described below in Example 2.

The careful comparison, microscopical and otherwise, of the products prepared in several different ways shows clearly the superiority of nitroguanidine prepared by the methods of this invention, particularly for nitroguanidine which is to be incorporated in propellant powders. Moreover, when prepared as herein described, a more uniform product is obtained, very little variation being exhibited from the maximum to the minimum crystal size.

The following examples are included herein in order to facilitate a more complete understanding of the invention. A number of variations in the process are included below in order to illustrate the extended scope of the procedure herein disclosed.

EXAMPLE 1 7 grams of coarse crystalline nitroguanidine was dissolved in about 100 cc. of water. Small portions of this solution, about 2 to 4 00., were withdrawn and mixed in a test tube with 1 to 3%, based on the nitroguanidine present, of ethylene diamine. The test tube was immersed in a beaker of boiling water until the nitroguanidine was completely dissolved. A portion of this solution was poured into a test tube containing dry ice. The precipitated crystalline nitroguanidine was examined microscopically in order to measure the length and cross-section of its individual crystals. The resultant crystals were predominantly of a very small size, namely about 2.5 microns wide by about microns long.

EXAMPLE 2 An aqueous solution of nitroguanidine of about 7.5% strength was prepared and from 1 to 3% of a modifying agent, such as ethylene diamine. was added. This solution was heated in an autoclave to about 100 C. and then sprayed into water having a temperature of 25 C. in an enclosed spray chamber. The precipitate formed was examined microscopically and showed a decided increase in the proportion of nitroguanidine crystals about 2.5 microns in width by about 5020 microns in length as compared to nitroguanidine precipitated from a similar solution but which, however, was prepared without the addition of ethylene diamine. The latter crystals were about 5 x 150 microns in size.

In the following examples an aqueous solution of nitroguanidine of 7.5% strength was prepared and. after adding the modifier indicated, the solution was heated to a temperature of 102 to 105 C. and spray cooled in a blo-wcase under a pressure of pounds per square inch.

w Particle size by number percent of total Example Modifier Width Length 2L5o 2.5-5.0).; 5.0 50 50-l00 100).

3 None (blankf) 30. 7 47. 7 21. 6 ,All about 15014. 4 1.0% ethylol dodecyl biguanide acetate 79. 4 20. 6 0. 0 76. 1 23. 9 0. 0

methylene triamine I 5 015% Triethylcne tetramine' 97.5 2.5 0.0 94.0 6.0 0.0

'Ietraethylene pentamina- I 6 0.4% ethylene diamiue 99. 9 0. l 0. 0 99. 2 0.8 0.0 7 0.3% ethylene'diamine. 85. 9 14.1 0.0 8. 0.36 ethylene diamine 87. 4 12. 4 0. 2 93. 5 6. 5 0.0 9 0.32% ethylene diamine 88. 6 11.2 0.2 90. l 9. 8 0. 0

These examples indicate that the percentage of crystal less than 2.5 microns wide by actual count was increased from 30.7 for the unmodified or "Blank example to 85.9 or more by the use of ethylene diamine. The mixed amines were almost as effective but required about twice as much modifier.

In the following examples each run consisted of a charge of 20.5 pounds of crude nitroguanidine and 275 pounds of water mixed in an autoclave at 100 C. The solution was then transferred to a blowcase and sprayed through inch jets into an enclosed spray chamber containing a circulating charge of 300 pounds of water. In order to accelerate the cooling of the batches to 25 C., air was drawn through the chamber at i the rate of 600 cu. ft. per minute. The temperature of the blowcase was held at l02-105 C. and the spraying pressure was maintained at 100 pounds per square inch. In each run, the crystal size was varied by the use of ethylene diamine of the strength indicated. This wa added to the charge and to the bath. The pH of the charge was adjusted with acetic, acid after the addition of the ethylene diamine. The precipitated nitroguanidine was separated from the residue by centrifugal action or by filtration and the crystalline product was subsequently washed with Water alone or, preferably, with water containing 0.1 percent of ethylol dodecyl biguanide acetate.

The residual mother liquor from each run was used to make up the next charge and batch, sufficient Water and ethylene diamine being added to compensate for that lost in the recrystallization and by evaporation.

EXAMPLE 10 Batch 1 [Width of crystals 4 microns] Wei ht of Per cent W'ci ht of Run No. ethylene di ethylene pH nitroamine used diamine guanidine Gr. Lbs.

EXAMPLE 11 Batch 2 [Width of crystals 3 microns] Weight of Per cent Weight of Run No. ethylene diethylene pH nitroarninc used diamine guanidine G1. Lbs.

By actual microscopical count the percentage EXAMPLE 12 Batch 3 [Width of crystals 5 microns] Weight of Percent Weight of Run No. ethylene ethylene pH nitroguanidiaminc used diarnine dine Lbs. 0,4 7.0 17 0. 4 7. 0 15 0.4 8. 0) 0.4 8.0) 15 0.3 8.0) 3.0 o. 4 8.0) 0.3 8.0 16 0. 3 8. 0 1G In addition to the preparation of nitroguanidine in the form of very finely divided discrete crystals by the process of this invention, various other substances can be prepared in a similarly minute crystalline condition. Thus mercury fulminate, lead azide, nitro amino guanidine and its salts, as Well as picri acid, tetranitraniline and the 1ike,can be prepared and a definite control of their minute crystalline shape, size and form can be effected with the aid of the various modifiers of crystal habit herein described.

Various methods can be used to effect the desired crystallization. For example, spray cooling chambers may be utilized or spraying the solution in the form of fine streams into, or preferably under, an ice-Water bath are among various other methods which can be used for the sudden cooling or chilling of solutions in order to precipitate the solute in finely divided form.

The very fine crystalline materials thus prepared find use in the manufacture of explosives. For example, a more highly effective type of explosive, namely a more powerful cordite, is obtained when such very fine crystals of nitroguanidine are used as can be prepared in accordance with the principles of this invention.

In particular, the use of such small crystals of nitroguanidine as above prepared in plastic cordite results in a greatly accelerated rate of propagation of the flame upon explosion and, moreover, it has been found that the oxidation of cordite is directly dependent upon the degree of subdivision of the crystalline nitroguanidine used. Thus, it has been definitely established that the small crystals of nitroguanidine produced in accordance with this invention are far more desirable for incorporation in cordite than the larger crystals heretofore used.

In addition to such modifying agents as the amino and similar nitrogen containing compounds given above, various others may be used. Among such compounds the following may be more specifically cited. These are classified as markedly effective, effective and slightly effective in the modification of crystalline habit.

A. Markedly efiective:

Ethylol dodecyl biguanide acetate Ethylol dodecyl biguanide hydrochloride Casein (dissolved in dilute NHiOH) Casein (dissolved in dilute sodium tetraphosphate solution) Corn 'oil condensed with :monoethylol :cyanamide 1.3 diethylol -butyl biguanide diacetate Di-ortho-tolyl guanidine Di-phenyl guanidine Di-xylyl guanidine (Di-ortho-tolyl guanidine) 4SnCl4 Ethylene diamine Ethylene diamine+acetic acid Ethylene diamine+HzSO4 Ethylene diamine+HCl Glue Mixed diethylene triamine, triethylene tetramine, and tetraethylene pentamine+acetic acid Mixed diethylene triamine, triethylene tetramine, and tetraethylene pentamine Phenyl biguanide 7 Soy bean fatty acids condensedwith monoethylol cyanamide Soy bean protein (dissolved in dilute sodium tetraphosphate solution) Tetraethylene pentamine+acetic acid B. Effective:

(Di-ortho-tolyl guanidine) 2ZI1C12 '(Diaryl dithiophosphoric acids)+thiocarbanilide Ethylol dodecyl guanidine acetate Hexa or octadecyl guanidine acetate Sodium salt of diisopropyl dioctyl sulfosuccinic acid-l-pine oil A12 (S04) 2 (diphenyl guanidine) s Castor oil fatty acids condensed with monoethylol cyanamides Corninaol (contains nitrogen) Cyanaceto guanamine a-2-cymel biguanide hydrochloride Cyanurea Ethylidene oc-O-tOlYl biguanide hydrochloride Furfural (mixed) Xylol biguanide I Gelatin Glutarnic acid Glycine Guanidine thiocyanate B-Methoxy butyro guanamine Methylene o-tolyl biguanide Monoethylol cyanamide condensed with ethylene diamine Phenyl biguanide carbonate Pyridine: I-IBr iii-Tertiary amyl phenyl biguanide hydrochloride a-Mixed Xylyl biguanide hydrochloride C. Slightly efiective:

Acetamidine anthranilate p Amino acetophenon Benzylidene a-tolyl biguanide hydrochloride Benzoguanamine-2-sulfonic acid Black Liquor Soap condensed with monoethylol cyanamide Sec. butyl phenyl bigu-anide hydrochloride o-Carbamyl benzoguanamine Coconut oil-polyethylene amines condensed with same Corn sugar 'Dextrin Diethanol amine Dimethylol urea Ethylidene oc- (sec. butyl phenyDbiguanide hydrochloride Ethylidene oc-(O-tOlYl) biguanide hydrochloride fi-Ethoxy butyrc guanamine lGuanidine carbonate+acetic acid Guanidine carbonate Thus, the general efiect of such modificationrof crystal habit cannot be definitely attributed to any specific group and/ or groups of elements, nor is it limited to either organic or inorganic compounds.

No completely satisfactory theoretical explanation of the manner in which these modifying agents function, other than that above given, can be offered. Moreover the modifying agents themselves do not fall within any recognized class, or appear to have any property in common other than their ability to change the crystal habit of nitroguanidines and substances similar therewith so as to yield extraordinarily small crystals.

It is to be understood that the examples, although drawn to the preparation of finel crystalline nitroguanidine are not to be deemed limited thereto. The invention in its broader aspects embraces the treatment, by the above described process, of various other organic compounds which are relativel soluble at higher temperatures such as those of boiling water and other boiling solvents and which when cooled form supersaturated solutions which readily precipitate outthe solute in crystalline form. For these reasons the descriptive examples are to be taken as specific illustrations of the principles of the invention which is to be limited solely by the scope of the appended claims.

We claim:

1. The method of preparing finely divided nitroguanidine which comprises forming an aqueous solution of nitroguanidine at a temperature above C. but below the decomposition temperature of nitroguanidine, adding from 0.3 to 3% of ethylene diamine and cooling the solution to precipitate the nitroguanidine in a finely divided form.

2. The method of preparing finely divided nitroguanidine which comprises forming a saturated solution of nitroguanidine in boiling water, adding from 0.3 to 3% of ethylene diamine and cooling the solution to precipitate the nitroguanidine in a finely divided form.

3. The method of preparing crystalline nitroguanidine of the order of at most 2.5 to 5 microns in width and 20 to microns in length which comprises preparing a hot aqueous solution of nitroguanidine, adding from 1 to 3% of ethylene diamine and cooling the solution to precipitate the nitroguanidine in a finely divided form.

GEORGE I-l'. FOSTER. EMIL F. WILLIAMS. 

